On social media, it's been nearly impossible to escape the Ice Bucket Challenge videos and photos of people dumping ice water over their heads.

The feel-good campaign has raised $15.6 million since July 29 for the ALS Association, which researches Amyotrophic lateral sclerosis, also known as Lou Gehrig's disease. That's compared with $1.8 million raised in the same time period last year.

But the online campaign has also been criticized as "slacktivism" — online engagement for a cause that requires very little time, effort or real-world involvement.

Some critics of slacktivism — also called "clicktivism" or "hashtag activism" — question whether people who have dumped water over their heads have donated money or even know what ALS is.

"A lot of the participants are probably spending more money on bagged ice than on ALS research," wrote Will Oremus in Slate.

Activist groups say they use social media because they can "meet people where they are," said Jonathan Obar, an assistant professor of communications studies at the University of Ontario Institute of Technology.

Even if someone doesn't donate money, slacktivism, at the very least, raises awareness around a cause, Obar said.

"One of the great things about social media is it creates more of a conversation ... as opposed to the one-way, watch our PSAs or read our mailers," Obar said. "It's a conversation that can lead to more engagement."

Tambra Stucky has a bucket of ice water poured on her head by son Keelan, 11, while participating in the ALS Ice Bucket Challenge on Aug. 16 in Pretty Prairie, Kan.(Photo: Lindsey Bauman, AP)

Is awareness enough?

After tweeting or posting to Facebook, how many people take action in a meaningful, tangible way?

The negative portrayal of slacktivism was captured in a UNICEF campaign last year in Sweden. In an online ad, the organization said, "Like us on Facebook and we will vaccinate zero children against Polio."

Research this year from Canada found the more public a person's activism is online, the less likely they are to act in a meaningful way.

"By publicly supporting these causes, you say, I'm a good person," diminishing the need to provide follow-up support for the cause, said Kirk Kristofferson, a Ph.D. candidate in marketing at the University of British Columbia's Sauder School of Business.

If a non-profit thinks that a public declaration of support leads to meaningful support, "we find that this belief may not be accurate," according to the summary to Kristofferson's April 2014 paper published in the Journal of Consumer Research.

Another study found that people who sign an online petition are more likely to donate money to that cause. It also found that people who don't sign the petition donate "significantly more" money to an unrelated cause, according to the 2013 study entitled, "Does Slacktivism Hurt Activism?"

Social media activism isn't replacing traditional methods but is rather "supplementing" them, said Julie Dixon, deputy director of the Center for Social Impact Communication.

How sustainable is the campaign?

The challenge isn't just how to create the next Ice Bucket Challenge, but how to keep that attention.

"That's the thing with the social media animal: It's an amazing organism, but its lifeblood is user content and user participation," Obar said. "Without the lifeblood, the organism dies."

Causes that have captured people's attention can keep people engaged by providing updates and communicating how the donations have been spent, Dixon said.

"If people plainly see the dollars translate into a measurable impact, they're more likely to give again," she said.

With the Ice Bucket Challenge, the ALS Association has no expectations of how long the phenomenon will last, but so far the exposure alone has been "so incredibly invaluable," said Carrie Munk, spokeswoman for the ALS Association.